Method for treating livestock and poultry wastewater by micro-electrolysis series double-cathode coupling system

Abstract

The invention discloses a method for treating livestock and poultry wastewater by a micro-electrolysis series double-cathode coupling system. The method comprises the following steps: homogenizing livestock and poultry wastewater, and enabling the livestock and poultry wastewater to enter an iron-carbon micro-electrolysis tank after the livestock and poultry wastewater is homogenized; effluent enters an electrolytic bath for electrolysis; the electrolytic bath comprises a first cathode, a first anode, a second cathode and a second anode; the first cathode is a crack gas diffusion electrode; the second cathode comprises a conductive substrate and a FeOCl catalyst coated on the conductive substrate; and effluent of the electrolytic cell is subjected to coagulating sedimentation and then is discharged. According to the method, part of organic pollutants in the wastewater are removed through Fe / C micro-electrolysis, the biodegradability of the wastewater is improved, the chromaticity of the wastewater is reduced, and Fe < 2 + > is provided for a subsequent Fenton oxidation pond; h2O2 is efficiently produced through the crack gas diffusion electrode, OH is efficiently produced through efficient activation of the FeOCl / GF composite electrode, advanced oxidation treatment is conducted on the wastewater, other auxiliary devices do not need to be matched, the product is environmentally friendly and free of secondary pollution, and efficient degradation of the livestock and poultry wastewater can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly to a method for treating livestock and poultry wastewater by a microelectrolysis tandem dual-cathode coupling system. Background Art

[0002] Livestock and poultry breeding wastewater mainly contains pollutants such as nitrogen, phosphorus, and antibiotics. If not properly treated, it will have a serious impact on the ecological environment. Therefore, the task of purifying livestock and poultry breeding wastewater and protecting environmental water resources is urgent. However, how to efficiently treat livestock and poultry breeding wastewater is still a research hotspot in the field of water treatment.

[0003] Hydrogen peroxide (H2O2) is a zero-emission and highly efficient chemical oxidant, which is widely used in the field of industrial water treatment. At present, more than 95% of commercial H2O2 is industrially produced by the anthraquinone method. Although the anthraquinone method has mature technology and perfect infrastructure, it still has significant disadvantages, such as high operating costs, dangerous explosion problems, and transportation restrictions. In recent years, the production of H2O2 through the two-electron oxygen reduction reaction [ORR, O2 + 2H + + 2e - → H2O2] has been proven to be a cost-effective alternative to traditional chemical methods, avoiding the need for transportation, storage, and handling of concentrated H2O2.

[0004] The in-situ electrochemical production of H2O2 depends on effective oxygen supply. In an in-situ H2O2-producing electrochemical system, due to the difference in the number of electron transfers between the anode (four-electron OER process) and the cathode (two-electron ORR process), the oxygen consumed by the cathode to produce H2O2 is twice that of traditional methods. Although injecting oxygen into water is feasible, this process requires additional installation work of oxygen supply equipment and energy consumption. In addition, during the two-electron ORR process, the rapid electro-wetting induced by high current will damage the initial gas capture channels of the electrode, resulting in O2 starvation at the electroactive interface, thereby reducing the reaction efficiency of in-situ electrochemical production of H2O2.

[0005] How to apply the in-situ electrochemically produced H2O2 to the field of industrial water treatment involves the electrochemical advanced oxidation process (AO). Those technologies based on the Fenton reaction chemistry, such as electro-Fenton (EF), have been proven to be the most robust technologies. For example, a carbon-based self-breathing cathode for in-situ production of hydrogen peroxide and degradation of organic matter and its preparation method disclosed in Patent CN117721490A. The EF reaction lies in the production of strongly oxidizing hydroxyl radicals (OH), through the Fenton reaction between hydrogen peroxide (H2O2) generated by the cathode and an externally added Fe 2+ catalyst. However, conventional homogeneous EF methods have disadvantages such as a narrow working pH window (2.8 - 3.5) and the formation of iron sludge. Summary of the Invention

[0006] The present invention aims to overcome the above problems existing in the prior art, and provides a method for treating livestock and poultry wastewater by a micro-electrolysis series double-cathode coupling system. First, Fe / C micro-electrolysis pretreatment is carried out to remove some organic pollutants in the wastewater, improve the biodegradability of the wastewater, and reduce the chromaticity of the wastewater, so as to provide Fe for the subsequent Fenton oxidation tank. 2+ Then, through the double-cathode GDE in-situ electro-Fenton device, H2O2 is efficiently produced through the crack gas diffusion electrode, and then high-efficient activation of FeOCl / GF composite electrode is carried out to produce ·OH for advanced oxidation treatment of the wastewater. There is no need to cooperate with other auxiliary devices such as oxygen supply devices. The products are green and environmentally friendly and have no secondary pollution. This process method can achieve the efficient degradation of livestock and poultry wastewater.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A method for treating livestock and poultry wastewater by a micro-electrolysis series double-cathode coupling system, the steps include: (1) Homogenize and equalize the livestock and poultry wastewater, and then enter the iron-carbon micro-electrolysis cell for micro-electrolysis reaction; (2) The effluent from the iron-carbon micro-electrolysis cell enters the electrolytic cell for electrolysis reaction; The electrolytic cell includes a first cathode, a first anode, a second cathode, and a second anode arranged alternately; The first cathode and the second cathode include a conductive substrate and a catalyst coated on the conductive substrate. The catalysts of the first cathode and the second cathode are carbon black-PTFE catalyst and FeOCl catalyst respectively; the first cathode is a crack gas diffusion electrode; The first anode is an MMO mixed metal electrode or a ruthenium-iridium electrode; The second anode is a diamond electrode; (3) The effluent after the electrolysis reaction is subjected to coagulation precipitation and then discharged.

[0008] The present invention first balances the water quality and water volume of the livestock and poultry wastewater, and then enters the iron-carbon micro-electrolysis cell. Through Fe / C micro-electrolysis pretreatment, some organic pollutants in the wastewater are removed, the biodegradability of the wastewater is improved, the chromaticity of the wastewater is reduced, and Fe is provided for the subsequent Fenton oxidation tank. 2+ Then it enters the electrolytic cell. The electrolytic cell of the present invention adopts a double-cathode GDE in-situ electro-Fenton device, and H2O2 is efficiently produced through the crack gas diffusion electrode. Then high-efficient activation of FeOCl / GF composite electrode is carried out to produce ·OH for advanced oxidation treatment of the wastewater; finally, the suspended organic matter is flocculated and precipitated in the coagulation sedimentation tank, and then the water is discharged.

[0009] The main reaction formulas in the wastewater degradation process in the electrolytic cell of the present invention are as follows: Near the first cathode: Cathode:O2+2H ++2e - →H2O2 (1); Near the first anode: Anode: 2H2O - 4e - →O2 + H + (2); Near the second anode: Cathode: Fe(III) + ·OH → Fe(IV) + OH - (3); Fe(IV) + ·OH → Fe(V) + OH - (4); Near the second cathode: Anode: Fe 2+ + H2O2 → [Fe(OH)2] 2+ → ·OH + OH - + Fe 3+ (5); Organic pollutants + ·OH → Degradation products (6); Fe 3+ + e - → Fe 2+ (7).

[0010] In the present invention, oxygen is produced by the first anode MMO, and then the crack gas diffusion electrode is used as the first cathode to produce H2O2; the O2 generated by the anodic oxygen evolution (OER) reaction of electrochemically in-situ producing H2O2 is used to supply oxygen to the first cathode to realize in-situ self-supply of oxygen to produce hydrogen peroxide. In this process, no additional oxygen supply is required, reducing the work and energy consumption. At the same time, the present invention adopts a crack gas diffusion electrode to overcome the electrowetting effect during long-term electrolysis under harsh industrial-related conditions. Even under harsh electrolysis conditions, due to the weakening of the local electric field and liquid infiltration capillary force caused by spatial discontinuity, these micron-scale film defects can counterintuitively maintain strong superhydrophobicity, enabling O2 to freely and rapidly diffuse in these channels. The second cathode of the present invention uses FeOCl as a catalyst. Iron oxychloride (FeOCl) is a two-dimensional layered metal oxychloride with high electron mobility and electron delocalization properties. It can not only efficiently activate and produce ·OH, electrochemically reduce Fe 3+ to generate Fe 2+ , but also has high pH adaptability.

[0011] Therefore, a self-oxygen-supplying in-situ hydrogen peroxide-producing - FeOCl dual-cathode system is constructed in the electrolytic cell of the present invention: the first cathode uses a carbon black (CB)-PTFE / GF cracked gas diffusion electrode, and the gas diffusion layer of this electrode can efficiently utilize oxygen, thereby realizing a two-electron reaction and efficiently producing H2O2 in-situ. The second cathode uses a FeOCl / GF composite electrode, which can not only efficiently activate and produce ·OH, but also electro-reduce Fe 3+ to avoid the generation of iron sludge. The dual-cathode system of the present invention uses electro-Fenton to efficiently treat wastewater, without the need to cooperate with other auxiliary devices such as an oxygen supply device. The products are green and environmentally friendly and have no secondary pollution, and can achieve the efficient degradation of livestock and poultry wastewater.

[0012] Preferably, the livestock and poultry wastewater in step (1) is homogenized and equalized in the regulating tank, and the hydraulic retention time of the regulating tank is 25 - 35 min.

[0013] Preferably, in the iron-carbon micro-electrolysis cell of step (1), the mass ratio of iron to carbon is 2.5 - 3.5:1; the total mass of iron and carbon is 30 - 40% of the mass of the wastewater.

[0014] Preferably, the hydraulic retention time of the iron-carbon micro-electrolysis cell in step (1) is 1 - 3 h.

[0015] Preferably, the conductive matrix in the first cathode and the second cathode of step (2) is one of carbon paper, carbon fiber paper, carbon cloth, carbon fiber cloth, graphite felt, nickel foam, copper foam, titanium plate, ruthenium-iridium electrode plate, and conductive glass.

[0016] Preferably, in the carbon black-PTFE catalyst of the first cathode in step (2), the mass ratio of carbon black to PTFE is 5:2 - 4; the loading amount of carbon black in the first cathode is 5 - 40 mg / cm 2 .

[0017] Preferably, the loading amount of the FeOCl catalyst in the second cathode of step (2) is 5 - 40 mg / cm 2 .

[0018] Preferably, the hydraulic retention time of the electrolytic cell in step (2) is 2 - 4 h.

[0019] Preferably, in step (3), a coagulant is added to the effluent of the electrolytic cell for a coagulation reaction, and the dosage of the coagulant is 10 - 30 mg / L.

[0020] Preferably, the coagulation and sedimentation time in step (3) is 1 - 3 h.

[0021] Therefore, the present invention has the following beneficial effects: (1) The device has a simple structure and is easy to operate. Moreover, all reaction processes are completed in a single reaction device without the need for other auxiliary equipment, resulting in low operation and maintenance costs. (2) The first cathode used in the device is a CB-PTFE / GF crack gas diffusion electrode. The gas diffusion layer of this electrode can efficiently utilize oxygen, thereby achieving a 2-electron reaction and in-situ high-efficiency production of H2O2. (3) The second cathode used in the device is a FeOCl / GF composite electrode, which can not only efficiently activate to produce ·OH, but also electro-reduce Fe 3+ to avoid the generation of iron sludge and realize the recycling of iron ions at the same time. (4) The device has a high degradation efficiency. The removal rates of total nitrogen, total phosphorus, COD, chromaticity, and total suspended solids in livestock and poultry wastewater reach over 80%. The reaction product is water without harmful by-products, meeting the current clean energy theory. (5) Treating wastewater through the system of the present invention not only achieves high-efficiency zero discharge, but also greatly reduces the corresponding traditional treatment costs. Brief Description of the Drawings

[0022] Figure 1 is the flow chart of the present invention; Among them, 1 - water storage tank, 2 - first inlet water pump, 3 - regulation tank, 4 - second inlet water pump, 5 - iron-carbon micro-electrolysis cell, 6 - third inlet water pump, 7 - electrolytic cell, 8 - first anode, 9 - first cathode, 10 - polymer ion exchange membrane, 11 - second anode, 12 - second cathode, 13 - external power supply, 14 - fourth inlet water pump, 15 - coagulation sedimentation tank.

[0023] Figure 2 is the graph of the changes in total solids, total suspended solids, total dissolved solids, and chromaticity in the process flow of Example 1.

[0024] Figure 3 is the graph of the changes in ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and Fe 2+ concentration in the process flow of Example 2.

[0025] Figure 4 is the graph of the changes in COD, BOD, total nitrogen, and total phosphorus in the process flow of Example 3.

[0026] Figure 5 is the graph of the changes in COD, total nitrogen, total phosphorus, and Fe 2+ concentration in the electrolytic cell of Example 4. Detailed Embodiments

[0027] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0028] In the present invention, unless otherwise specified, all devices and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following examples are conventional methods in the art unless otherwise specified.

[0029] General embodiment: A method for treating livestock and poultry wastewater by a micro-electrolysis tandem dual-cathode coupling system, the process is as Figure 1 shown, and the steps include: (1) The livestock and poultry wastewater enters the storage tank 1 for storage, and then enters the adjustment tank 3 through the first feed pump 2 for homogenization and equalization of quantity. (2) The effluent from the adjustment tank enters the iron-carbon micro-electrolysis cell 5 through the second feed pump 4 for micro-electrolysis reaction. (3) The effluent from the iron-carbon micro-electrolysis cell enters the electrolytic cell 7 through the third feed pump 6 for electrolysis reaction. The electrolytic cell includes a first anode 8, a first cathode 9, a second anode 11, and a second cathode 12 arranged alternately; the first cathode and the second anode are separated by a polymer ion exchange membrane 10; the first anode and the second anode are connected to the positive pole of the external power supply 13, and the first cathode and the second cathode are connected to the negative pole of the external power supply. The first cathode is a crack gas diffusion electrode, which includes a conductive matrix and a carbon black-PTFE catalyst coated on the conductive matrix. The first anode is an MMO mixed metal electrode or a ruthenium-iridium electrode. The second cathode includes a conductive matrix and a FeOCl catalyst coated on the conductive matrix. The second anode is a diamond electrode. (4) The effluent from the electrolytic cell enters the coagulation sedimentation tank 15 through the fourth feed pump 14 for sedimentation and then the water is discharged.

[0030] In the present invention, the livestock and poultry wastewater is first balanced in terms of water quality and quantity in the adjustment tank, and then enters the iron-carbon micro-electrolysis cell. After the Fe / C micro-electrolysis pretreatment, part of the organic pollutants in the wastewater are removed, the biodegradability of the wastewater is improved, and the chromaticity of the wastewater is reduced, providing Fe for the subsequent Fenton oxidation tank 2+ ; then it enters the electrolytic cell. The electrolytic cell of the present invention adopts a dual-cathode GDE in-situ electro-Fenton device. Through the crack gas diffusion electrode, H2O2 is efficiently produced, and then through the FeOCl / GF composite electrode, ·OH is efficiently activated to carry out advanced oxidation treatment on the wastewater; finally, the suspended organic matter is flocculated and precipitated in the coagulation sedimentation tank, and then the water is discharged.

[0031] As a specific embodiment, the hydraulic retention time of the adjustment tank in step (1) is 25 to 35 minutes.

[0032] As a specific implementation manner, in the iron-carbon microelectrolysis cell of step (2), the mass ratio of iron to carbon is 2.5 - 3.5:1; the total mass of iron and carbon is 30 - 40% of the mass of the wastewater.

[0033] As a specific implementation manner, the hydraulic retention time of the iron-carbon microelectrolysis cell in step (2) is 1 - 3 h.

[0034] As a specific implementation manner, the conductive matrix in the first cathode and the second cathode of step (3) is one of carbon paper, carbon fiber paper, carbon cloth, carbon fiber cloth, graphite felt, nickel foam, copper foam, titanium plate, ruthenium-iridium electrode plate, and conductive glass.

[0035] As a specific implementation manner, in the carbon black-PTFE catalyst of the first cathode in step (3), the mass ratio of carbon black to PTFE is 5:2 - 4; the loading amount of carbon black in the first cathode is 5 - 40 mg / cm 2 。

[0036] As a specific implementation manner, the preparation method of the first cathode is as follows: Mix carbon black with absolute ethanol and perform ultrasonic oscillation, then add the PTFE suspension, stir at 60 - 80 °C until it becomes a paste to obtain a coating; coat the coating on the conductive matrix, and then calcine it at 330 - 400 °C for 150 - 200 min to obtain a cracked gas diffusion electrode.

[0037] As a specific implementation manner, the loading amount of the FeOCl catalyst in the second cathode of step (3) is 5 - 40 mg / cm 2 。

[0038] As a specific implementation manner, the preparation method of the second cathode is as follows: First, dissolve FeCl3·6H2O in absolute ethanol and perform ultrasonic oscillation to form a uniform ferric chloride solution; then immerse GF in the ferric chloride solution, take it out and dry it, transfer it to a sealed crucible, and calcine it at 210 - 230 °C for 1 - 2 hours; after cooling to room temperature, wash the electrode repeatedly with absolute ethanol and deionized water and then dry it; finally, soak the electrode in the PTFE suspension, and then calcine it at 170 - 190 °C for 1 - 2 hours to finally obtain the second cathode.

[0039] As a specific implementation manner, the hydraulic retention time of the electrolytic cell in step (3) is 2 - 4 h.

[0040] As a specific implementation manner, a coagulant is added to the coagulation sedimentation tank in step (4) for coagulation reaction, and the dosage of the coagulant is 10 - 30 mg / L.

[0041] As a specific implementation manner, the hydraulic retention time of the coagulation sedimentation tank in step (4) is 1 - 3 h.

[0042] Example 1: A method for treating livestock and poultry wastewater by a micro - electrolysis series double - cathode coupling system, the steps include: (1) Take 8L of livestock and poultry wastewater and store it in a reservoir, then enter the regulating tank through the first feed pump for homogenization and equalization. The hydraulic retention time of the regulating tank is 30min; (2) The effluent from the regulating tank enters the iron - carbon micro - electrolysis cell through the second feed pump for micro - electrolysis reaction; in the iron - carbon micro - electrolysis cell, the mass ratio of iron to carbon is 3:1; the total mass of iron and carbon is 35% of the mass of the wastewater, and the hydraulic retention time of the iron - carbon micro - electrolysis cell is 2h; (3) The effluent from the iron - carbon micro - electrolysis cell enters the electrolytic cell through the third feed pump for electrolysis reaction. The hydraulic retention time of the electrolytic cell is 3h; The electrolytic cell includes a first anode, a first cathode, a second anode, and a second cathode arranged alternately; the first cathode and the second anode are separated by a polymer ion - exchange membrane; the first anode and the second anode are connected to the positive pole of an external power supply, and the first cathode and the second cathode are connected to the negative pole of the external power supply; The first cathode is a CB - PTFE / GF crack gas diffusion electrode, including a conductive matrix graphite felt (GF) and a carbon black - PTFE catalyst coated on the conductive matrix; the preparation method is: mix carbon black with absolute ethanol, ultrasonic oscillation, then add PTFE suspension (solid content 5wt%), stir at 70 °C until it becomes paste - like to obtain a coating, and the mass ratio of carbon black to PTFE is 5:3; coat the coating on the graphite felt, and then calcine at 350 °C for 180min to obtain the CB - PTFE / GF crack gas diffusion electrode; the loading amount of carbon black in the first cathode is 29.1mg / cm 2 ; The first anode is an MMO mixed metal electrode; The second cathode is an FeOCl / GF composite electrode, including a conductive matrix graphite felt (GF) and an FeOCl catalyst coated on the conductive matrix; the preparation method is: first dissolve FeCl3·6H2O in absolute ethanol and ultrasonic for 10 minutes to form a uniform ferric chloride solution; then immerse GF in the ferric chloride solution for 1 hour and take it out for drying, transfer it to a sealed crucible, and calcine at 220 °C for 1 hour; after cooling to room temperature, wash the electrode repeatedly with absolute ethanol and deionized water, and dry it in a 50 °C vacuum drying oven for 12 hours; finally, immerse the electrode in PTFE suspension (solid content 5wt%) for 30 minutes, and then calcine at 180 °C for 1 hour to finally obtain the second cathode with the loading amount of the FeOCl catalyst being 4.2mg / cm 2 ; The second anode is a diamond (BDD) electrode; The areas of the first cathode and the second cathode are both 9.62cm 2, the areas of the second anode and the second anode are both 2 cm 2 ; (4) The effluent from the electrolytic cell enters the coagulation sedimentation tank through the fourth inlet pump, and after adding the coagulant PAC for coagulation sedimentation, the effluent is discharged. The dosage of the coagulant is 20 mg / L, and the hydraulic retention time of the coagulation sedimentation tank is 2 h.

[0043] Take the effluents from the regulating tank, the iron-carbon micro-electrolytic cell, the electrolytic cell and the coagulation sedimentation tank, and measure their total solids, total suspended solids, total dissolved solids and chromaticity. The results are as Figure 2 shown below.

[0044] Example 2: A method for treating livestock and poultry wastewater by a micro-electrolysis series double-cathode coupling system, the steps include: (1) Take 8 L of livestock and poultry wastewater and store it in a reservoir, and then enter the regulating tank through the first inlet pump for homogenization and equalization. The hydraulic retention time of the regulating tank is 30 min; (2) The effluent from the regulating tank enters the iron-carbon micro-electrolytic cell through the second inlet pump for micro-electrolysis reaction; in the iron-carbon micro-electrolytic cell, the mass ratio of iron to carbon is 2.5:1; the total mass of iron and carbon is 40% of the mass of the wastewater, and the hydraulic retention time of the iron-carbon micro-electrolytic cell is 3 h; (3) The effluent from the iron-carbon micro-electrolytic cell enters the electrolytic cell through the third inlet pump for electrolysis reaction. The hydraulic retention time of the electrolytic cell is 3 h; The electrolytic cell includes a first anode, a first cathode, a second anode and a second cathode arranged alternately; the first cathode and the second anode are separated by a polymer ion exchange membrane; the first anode and the second anode are connected to the positive pole of an external power supply, and the first cathode and the second cathode are connected to the negative pole of the external power supply; The first cathode is a CB-PTFE / GF crack gas diffusion electrode, which includes a conductive matrix graphite felt (GF) and a carbon black-PTFE catalyst coated on the conductive matrix; the preparation method is: mix carbon black with absolute ethanol, ultrasonic oscillation, and then add a PTFE suspension (solid content 5 wt%), stir at 70 °C until it becomes paste-like to obtain a coating, and the mass ratio of carbon black to PTFE is 5:3; coat the coating on the graphite felt, and then calcine at 350 °C for 180 min to obtain the CB-PTFE / GF crack gas diffusion electrode; the loading amount of carbon black in the first cathode is 29.1 mg / cm 2 ; The first anode is a MMO mixed metal electrode; The second cathode is a FeOCl / GF composite electrode, which includes a conductive matrix graphite felt (GF) and a FeOCl catalyst coated on the conductive matrix; the preparation method is as follows: First, dissolve FeCl3·6H2O in absolute ethanol and ultrasonicate for 10 minutes to form a uniform ferric chloride solution; then immerse the GF in the ferric chloride solution for 1 hour, take it out and dry it, transfer it to a sealed crucible, and calcine it at 220 °C for 1 hour; after cooling to room temperature, wash the electrode repeatedly with absolute ethanol and deionized water, and dry it in a vacuum drying oven at 50 °C for 12 hours; finally, immerse the electrode in a PTFE suspension (solid content 5 wt%) for 30 minutes, and then calcine it at 180 °C for 1 hour to finally obtain a second cathode with a FeOCl catalyst loading of 4.2 mg / cm 2 ; The second anode is a diamond (BDD) electrode; The areas of the first cathode and the second cathode are both 9.62 cm 2 , and the areas of the second anode and the second anode are both 2 cm 2 ; (4) The effluent from the electrolytic cell enters the coagulation sedimentation tank through the fourth inlet pump, and after adding the coagulant PAC for coagulation sedimentation, the effluent is discharged. The dosage of the coagulant is 25 mg / L, and the hydraulic retention time of the coagulation sedimentation tank is 2 h.

[0045] Take the effluents from the regulating tank, the iron-carbon microelectrolysis cell, the electrolytic cell and the coagulation sedimentation tank, and measure their ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, Fe 2+ contents. The results are as Figure 3 shown.

[0046] Example 3: A method for treating livestock and poultry wastewater by a microelectrolysis series double-cathode coupling system, the steps include: (1) Take 8 L of livestock and poultry wastewater and store it in a reservoir, and then enter the regulating tank through the first inlet pump for homogenization and equalization. The hydraulic retention time of the regulating tank is 30 min; (2) The effluent from the regulating tank enters the iron-carbon microelectrolysis cell through the second inlet pump for microelectrolysis reaction; in the iron-carbon microelectrolysis cell, the mass ratio of iron to carbon is 3.5:1; the total mass of iron and carbon is 30% of the mass of the wastewater, and the hydraulic retention time of the iron-carbon microelectrolysis cell is 2 h; (3) The effluent from the iron-carbon microelectrolysis cell enters the electrolytic cell through the third inlet pump for electrolysis reaction. The hydraulic retention time of the electrolytic cell is 3 h; The electrolytic cell includes a first anode, a first cathode, a second anode, and a second cathode arranged alternately; the first cathode and the second anode are separated by a polymer ion exchange membrane; the first anode and the second anode are connected to the positive pole of an external power supply, and the first cathode and the second cathode are connected to the negative pole of the external power supply; The first cathode is a CB-PTFE / GF cracked gas diffusion electrode, which includes a conductive matrix graphite felt (GF) and a carbon black-PTFE catalyst coated on the conductive matrix. The preparation method is as follows: Mix carbon black with absolute ethanol and perform ultrasonic oscillation, then add a PTFE suspension (solid content 5wt%), stir at 70 °C until it becomes a paste to obtain a coating material. The mass ratio of carbon black to PTFE is 5:3. Coat the coating material on the graphite felt, and then calcine it at 350 °C for 180 min to obtain the CB-PTFE / GF cracked gas diffusion electrode. The loading amount of carbon black in the first cathode is 29.1 mg / cm 2 ; The first anode is an MMO mixed metal electrode; The second cathode is an FeOCl / GF composite electrode, which includes a conductive matrix graphite felt (GF) and an FeOCl catalyst coated on the conductive matrix. The preparation method is as follows: First, dissolve FeCl3·6H2O in absolute ethanol and perform ultrasonic treatment for 10 minutes to form a uniform ferric chloride solution. Then immerse the GF in the ferric chloride solution for 1 hour, take it out and dry it, transfer it to a sealed crucible, and calcine it at 220 °C for 1 hour. After cooling to room temperature, repeatedly wash the electrode with absolute ethanol and deionized water, and dry it in a vacuum drying oven at 50 °C for 12 hours. Finally, soak the electrode in a PTFE suspension (solid content 5wt%) for 30 minutes, and then calcine it at 180 °C for 1 hour to finally obtain the second cathode with the loading amount of the FeOCl catalyst being 4.2 mg / cm 2 ; The second anode is a diamond (BDD) electrode; The areas of the first cathode and the second cathode are both 9.62 cm 2 , and the areas of the second anode and the second anode are both 2 cm 2 ; (4) The effluent from the electrolytic cell enters the coagulation sedimentation tank through the fourth feed pump, and after adding the coagulant PAC for coagulation sedimentation, the effluent is discharged. The dosage of the coagulant is 15 mg / L, and the hydraulic retention time of the coagulation sedimentation tank is 3 h.

[0047] Take the effluents from the regulating tank, the iron-carbon micro-electrolytic cell, the electrolytic cell and the coagulation sedimentation tank, and measure their COD, BOD, total nitrogen and total phosphorus contents. The results are as Figure 4 shown.

[0048] Example 4: A method for treating livestock and poultry wastewater by a micro-electrolysis series double-cathode coupling system, the steps include: (1) Take 8 L of livestock and poultry wastewater and store it in a reservoir, then enter the regulating tank through the first feed pump for homogenization and equalization. The hydraulic retention time of the regulating tank is 25 min; (2) The effluent from the regulating tank enters the iron-carbon microelectrolysis cell through the second inlet pump for microelectrolysis reaction; in the iron-carbon microelectrolysis cell, the mass ratio of iron to carbon is 3:1; the total mass of iron and carbon is 30% of the mass of the wastewater, and the hydraulic retention time of the iron-carbon microelectrolysis cell is 2 h; (3) Adjust the pH value of the effluent from the iron-carbon microelectrolysis cell to 3, pump the effluent into the electrolytic cell, and circulate it at a constant flow rate of 400 mL / min. Carry out the electrolysis reaction under the condition of a current density of 10 mA·cm -2 . Do not pass oxygen in the electrolytic cell. Take samples of the solution in the electrolytic cell every half hour for the determination of COD, total nitrogen, total phosphorus, and Fe 2+ . The test results are as shown in Figure 5 . The electrolytic cell includes alternately arranged first anodes, first cathodes, second anodes, and second cathodes; the first cathode and the second anode are separated by a polymer ion exchange membrane; the first anode and the second anode are connected to the positive pole of the external power supply, and the first cathode and the second cathode are connected to the negative pole of the external power supply; The first cathode is a CB-PTFE / GF crack gas diffusion electrode, which includes a conductive matrix graphite felt (GF) and a carbon black-PTFE catalyst coated on the conductive matrix. The preparation method is as follows: Mix carbon black with absolute ethanol and ultrasonically oscillate it, then add PTFE suspension (solid content 5 wt%), stir it into a paste at 70 °C to obtain a coating, and the mass ratio of carbon black to PTFE is 5:3; coat the coating on the graphite felt, and then calcine it at 350 °C for 180 min to obtain the CB-PTFE / GF crack gas diffusion electrode; the loading amount of carbon black in the first cathode is 29.1 mg / cm 2 ; The first anode is an MMO mixed metal electrode; The second cathode is an FeOCl / GF composite electrode, which includes a conductive matrix graphite felt (GF) and an FeOCl catalyst coated on the conductive matrix. The preparation method is as follows: First, dissolve FeCl3·6H2O in absolute ethanol and ultrasonically vibrate it for 10 minutes to form a uniform ferric chloride solution; then immerse the GF in the ferric chloride solution for 1 hour and take it out to dry, transfer it to a sealed crucible, and calcine it at 220 °C for 1 hour; after cooling to room temperature, wash the electrode repeatedly with absolute ethanol and deionized water, and dry it in a vacuum drying oven at 50 °C for 12 hours; finally, immerse the electrode in PTFE suspension (solid content 5 wt%) for 30 minutes, and then calcine it at 180 °C for 1 hour to finally obtain the second cathode with a loading amount of FeOCl catalyst of 4.2 mg / cm 2 ; The second anode is a diamond (BDD) electrode; The areas of the first cathode and the second cathode are both 9.62 cm 2 , and the areas of the second anode and the second anode are both 2 cm2 .

[0049] From Figures 2 to 5 the results, it can be seen that when the method of the present invention is used to treat livestock and poultry wastewater, the removal rates of total nitrogen, total phosphorus, COD, chromaticity, and total suspended solids in the livestock and poultry wastewater reach over 80%, and the degradation efficiency is high. In the electrolytic cell of the present invention, oxygen is produced by the first anode MMO, and then the crack gas diffusion electrode is used as the first cathode to produce H2O2, thereby solving the problem of oxygen supply; the FeOCl / GF composite electrode is connected in series to efficiently treat wastewater by electro-Fenton. The reaction is completed in a single reaction device without the need to cooperate with other auxiliary devices, and the operation and operation costs are low; and the reaction product is water, without harmful by-products, and the product is green and environmentally friendly and has no secondary pollution, meeting the clean energy theory. Moreover, the second cathode of the present invention adopts the FeOCl / GF composite electrode, which can not only efficiently activate and produce ·OH, but also electro-reduce Fe 3+ to avoid the generation of iron mud and simultaneously realize the recycling of iron ions, and also has a high pH adaptability.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A method for treating livestock and poultry wastewater by a micro-electrolysis series double-cathode coupling system, characterized in that the steps Including: (1) Homogenize and equalize the livestock and poultry wastewater, and then enter the iron-carbon microelectrolysis cell for microelectrolysis reaction; (2) The effluent from the iron-carbon microelectrolysis cell enters the electrolytic cell for electrolysis reaction; The electrolytic cell includes a first cathode, a first anode, a second cathode, and a second anode arranged alternately; The first cathode and the second cathode include a conductive substrate and a catalyst coated on the conductive substrate. The catalysts of the first cathode and the second cathode are carbon black-PTFE catalyst and FeOCl catalyst respectively; the first cathode is a crack gas diffusion electrode; The first anode is an MMO mixed metal electrode or a ruthenium-iridium electrode; The second anode is a diamond electrode; (3) The effluent after the electrolysis reaction is subjected to coagulation precipitation and then discharged.

2. The method for treating livestock and poultry wastewater by the micro-electrolysis series double-cathode coupling system according to claim 1, wherein In step (1), the livestock and poultry wastewater is homogenized and equalized in the regulating tank, and the hydraulic retention time of the regulating tank is 25-35 min.

3. The method for treating livestock and poultry wastewater by the micro-electrolysis series double-cathode coupling system according to claim 1, characterized in that, In the iron-carbon microelectrolysis cell of step (1), the mass ratio of iron to carbon is 2.5-3.5:1; the total mass of iron and carbon is 30-40% of the mass of the wastewater.

4. The method for treating livestock and poultry wastewater by the microelectrolysis series double-cathode coupling system according to claim 1 or 2, characterized in that The hydraulic retention time of the iron-carbon microelectrolysis cell in step (1) is 1-3 h.

5. The method for treating livestock and poultry wastewater by the micro-electrolysis series double-cathode coupling system according to claim 1, characterized in that, The conductive substrate in the first cathode and the second cathode of step (2) is one of carbon paper, carbon fiber paper, carbon cloth, carbon fiber cloth, graphite felt, nickel foam, copper foam, titanium plate, ruthenium-iridium electrode plate, and conductive glass.

6. The method for treating livestock and poultry wastewater by the microelectrolysis series double-cathode coupling system according to claim 1, characterized in that In step (2), in the carbon black-PTFE catalyst of the first cathode, the mass ratio of carbon black to PTFE is 5:2 to 4; the loading amount of carbon black in the first cathode is 5 to 40 mg / cm 2 .

7. The method for treating livestock and poultry wastewater by the micro-electrolysis series double-cathode coupling system according to claim 1, characterized in that, In step (2), the loading amount of the FeOCl catalyst in the second cathode is 5 to 40 mg / cm 2 .

8. The method for treating livestock and poultry wastewater by the micro-electrolysis series double-cathode coupling system according to claim 1 or 5 or 6 or 7, characterized in that, The hydraulic retention time of the electrolytic cell in step (2) is 2-4 h.

9. The method for treating livestock and poultry wastewater by the micro-electrolysis series double-cathode coupling system according to claim 1, characterized in that, In step (3), a coagulant is added to the effluent from the electrolytic cell for coagulation reaction, and the dosage of the coagulant is 10-30 mg / L.

10. The method for treating livestock and poultry wastewater by the micro-electrolysis series double-cathode coupling system according to claim 1 or 9, characterized in that The coagulation precipitation time in step (3) is 1-3 h.

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